The present invention relates to an endoscope system for observing a fluorescing object, and more particularly to an endoscope system which emits excitation light towards an object to be observed, receives a fluorescent light emitted by the object, and display an image of the fluorescing object.
It has been known that, when organic tissues are illuminated by light having wavelengths of 420 nm through 480 nm, fluorescent substances included in the organic tissues such as NAHD, FMN fluoresce. By observing an image of the fluorescing organic tissues, a disorder of the organic tissue can be found. Specifically, light fluoresced by normal (i.e., not diseased) organic tissues includes more green component than a red component, while light fluoresced by organic tissues having a disorder includes less green component than the red component. Thus, based on the amount of the green fluorescent light, whether the organic tissues has a disorder can be determined.
The amount of the fluorescent light, however, varies depending on a distance between the organic tissue and a distal end of the endoscope. For example, if the distal end of the endoscope is relatively close to organic tissues having a disorder, the amount of the fluorescent light may be as much as that of organic tissues which do not have a disorder.
In order to avoid such a deficiency, in an endoscope utilizing the fluorescent light, diagnosis may be done based on a ratio of the green component of the fluorescent light to the red component.
In order to obtain the ratio of the green component to the red component, however, an imaging unit is required to include color filters for separating the red and green components from the fluorescent light, a pair of image intensifiers for the red and green components, and a pair of CCDs (Charge Coupled Devices) for the red and green components. Due to such a structure, the imaging unit becomes relatively large in size, and heavy, which lowers an operability of the endoscope. Further, due to a large number of elements, the endoscope utilizing the fluorescent light tends to be expensive.